Intriguing Discovery: Unique Mosasaur Species with Unusual “Screwdriver Teeth” Uncovered by Scientists

An artist’s rendering of the suspected appearance of Stelladens mysteriosus. Image provided by Dr. Nick Longrich.

A unique and rare mosasaur species has been found in Morocco by a team of scientists, which offers further insights into the rich diversity of these ancient marine reptiles that lived about 66 million years ago.

Researchers have discovered a distinctive species of mosasaur, an aquatic lizard from the dinosaur age, characterized by peculiar, ridged teeth, unlike any known reptile. This discovery, coupled with other recent archaeological finds from Africa, suggests that mosasaurs and similar aquatic reptiles underwent a swift evolutionary phase until roughly 66 million years ago. This period coincides with a devastating asteroid event that eradicated these creatures, dinosaurs, and nearly 90% of all Earth’s species.

Stelladens mysteriosus, the newly identified species from the Late Cretaceous period in Morocco, was approximately double the size of a dolphin.

Its dental structure was unique, consisting of blade-like ridges on the teeth, arranged in a star-like pattern, evoking the image of a Phillips-head screwdriver.

While most mosasaurs had two serrated, blade-like ridges on the tooth’s front and back for prey dissection, Stelladens had between four to six such blades running down each tooth. Image courtesy of Dr. Nick Longrich

“It’s unexpected,” commented Dr. Nick Longrich from the Milner Centre for Evolution at the University of Bath, the study’s leader. “It doesn’t resemble any known mosasaur, reptile, or even any vertebrate we’ve previously encountered.”

Dr. Nathalie Bardet, a marine reptile specialist from the Museum of Natural History in Paris, remarked: “In my 20+ years studying Moroccan mosasaurs, I’ve never encountered anything quite like this. It’s both baffling and fascinating!”

The presence of multiple teeth with the same peculiar shape implies that this unique form was not due to pathology or mutation.

The unique dental pattern hints at a specialized feeding technique or diet. However, the exact food that Stelladens consumed remains undetermined.

Dr. Longrich shared: “We can only speculate about this creature’s diet, as there’s nothing comparable in today’s world or the fossil record. The teeth resemble the tip of a Phillips-head screwdriver or possibly a hex wrench. As for its diet? Phillips head screws? IKEA furniture? It’s anyone’s guess.”

The fossils were unearthed in phosphate mines in Sidi Chennane, located in the southern Oulad Abdoun Basin, Morocco. Courtesy: Dr. Nick Longrich

Despite their small size, the teeth were robust and showed signs of wear at the tips, indicating that their diet didn’t include soft-bodied prey. The teeth weren’t strong enough to crush heavily armored prey like clams or sea urchins, though.

“Given these factors, it could have fed on small, lightly armored creatures like thin-shelled ammonites, crustaceans, or bony fish. It’s challenging to ascertain,” Longrich stated. “There were peculiar creatures in the Cretaceous period, such as ammonites, belemnites, and baculites, that no longer exist. Perhaps this mosasaur fed on an extinct species and occupied a niche that no longer exists. This might explain why we’ve never seen anything like this again.”

The mosasaurs lived alongside dinosaurs but were not dinosaurs themselves. Instead, they were giant lizards related to Komodo dragons, snakes, and iguanas, adapted for life in the ocean.

Mosasaurs emerged around 100 million years ago and diversified until about 66 million years ago, when a giant asteroid struck the Yucatan Peninsula in Mexico, plunging the world into darkness.

Recent discoveries from Morocco, including Stelladens, imply that mosasaurs were still evolving rapidly right until the end. It suggests that they didn’t fade away but met their end at their prime.

The ongoing study reveals that even after years of exploring the Moroccan Cretaceous, new species continue to be discovered, likely due to the rarity of most species.

According to the researchers, discovering all the rare species in a highly diverse ecosystem could take decades.

“We’re far from discovering everything in these layers,” said Longrich. “This is already the third new species unveiled just this year. The end-Cretaceous diversity is truly staggering.”

Professor Nour-Eddine Jalil from the Natural History Museum and a researcher at Univers Cadi Ayyad in Morocco, stated: “We’ve found an incredible range of surprises – mosasaurs with saw-like teeth, a turtle with a snout resembling a snorkel, and a variety of vertebrates of all shapes and sizes, and now a mosasaur with star-shaped teeth. It’s like the creations of an artist with an unlimited imagination.

“The sites in Morocco provide an unrivaled snapshot of the extraordinary biodiversity that existed just before the great Cretaceous crisis.”

Reference: “Stelladens mysteriosus: A Peculiar New Mosasaurid (Squamata) from the Maastrichtian (Late Cretaceous) of Morocco” by Nicholas R. Longrich, Nour-Eddine Jalil, Xabier Pereda-Suberbiola, and Nathalie Bardet, 17 May 2023, Fossils. DOI: 10.3390/fossils1010002

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More about Stelladens mysteriosus

• Study: “Stelladens mysteriosus: A Peculiar New Mosasaurid (Squamata) from the Maastrichtian (Late Cretaceous) of Morocco”
• University of Bath: Milner Centre for Evolution
• Museum of Natural History, Paris
• Univers Cadi Ayyad, Morocco
• Fossils Journal: “Stelladens mysteriosus: A Strange New Mosasaurid (Squamata) from the Maastrichtian (Late Cretaceous) of Morocco”